Reagents and methods for cyanobacterial production of bioplastics and biomaterials

ABSTRACT

The present invention provides reagents and methods for biomaterial production from cyanobacteria.

CROSS REFERENCE

This application claims priority to U.S. Patent Application Ser. No.60/937,400 filed Jun. 27, 2007, incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

In the coming decades, renewables are expected to gradually replacepetrochemical-based industrial products, including polymers. Productionof plastics from biopolymers offers the potential to replacenon-renewable materials derived from petroleum with renewable resources,resulting in reliable (domestic) supplies, jobs in rural communities,sustainable production, lower greenhouse gas production, and competitiveprices.

In response to an increased awareness of global environmental problems,PHA (Polyhydroxyalkanoates (PHA)) is gaining serious attention as apotential substitute for non-biodegradable polymers. The current rise ofthe oil and natural gas prices is reflected in the plastics market, andis making renewable bioplastics more competitive. However, prices of rawmaterials for the production of bioplastics based on bacterialfermentation are also increasing.

According to some reports, the cost of production of bioplastics bybacterial fermentation, especially when energy and materials consumedfor the production of fertilizers, pesticides, transport, and processenergy are factored in, is higher than that of photosyntheticallyproduced plastics, for which no raw material and fossil-fuel energy isrequired and that take up CO₂ from the environment. Thus, biopolymersproduced from autotrophic cyanobacteria that generate their ownfixed-carbon sources are likely to have an ever-increasing advantageover the production of biopolymers by fermentation.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides methods for producingbiomaterials, comprising:

(a) culturing cyanobacterial host cells that are deficient in Slr1125expression;

(b) harvesting the cyanobacterial host cells; and

(c) preparing biomaterials from the harvested cyanobacterial host cells.

The methods of the invention can be used, for example, to producequantities of biomaterials not previously possible using knowncyanobacterial host cells. In one embodiment the cyanobacterial hostcells have been genetically engineered to reduce or eliminate Slr1125expression. In another embodiment, the biomaterials comprisebiomaterials selected from the group consisting of polyhydroxyalkanoates(PHA) and cyanophycin. In a further embodiment, the cyanobacterial hostcells are selected from the group consisting of Synechocystis,Arthrospira maxima, Synechococcus, Trichodesmium; and Crocosphaera. Inanother embodiment, the cyanobacterial host cells are Synechocystis sp.PCC 6803 cells. In various further embodiments, the cyanobacterial hostcells have been recombinantly engineered to delete the slr1125 gene; thecyanobacterial host cells have been genetically engineered tooverexpress NAD synthetase and/or NAD+ kinase; the cyanobacterial hostcells are deficient in cyanophycin production; the cyanobacterial hostare deficient in expression of Slr1993; the cyanobacterial host cellsare deficient in cyanophycinase expression, and the cyanobacterial hostcells are recombinantly engineered to reduce or eliminate expression ofone or more of Slr1994, Slr1829, and Slr1830.

In a further aspect, the present invention comprises isolatedrecombinant nucleic acids, comprising:

(a) a first nucleic acid comprising an inducible cyanobacterialpromoter; and

(b) a second nucleic acid operably linked to the first nucleic acid,wherein the second nucleic acid encodes an inhibitory nucleic acidcomplementary to a target nucleic acid sequence that encodes an aminoacid sequence of a polypeptides selected from the group consisting ofSEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, and SEQ ID NO:8. The isolatednucleic acids of the invention can be used, for example, todown-regulate expression of Slr1125 in cyanobacterial cells, which isuseful, for example, in producing biomaterials according to the methodsof the present invention. In one embodiment, the inhibitory nucleic acidcomprises and antisense nucleic acid. In another embodiment, the targetnucleic acid sequence is selected from the group consisting of SEQ IDNO:1, SEQ ID NO:3, SEQ ID NO:5, and SEQ ID NO:7. In a furtherembodiment, the inducible cyanobacterial promoter comprises SEQ ID NO:9.In a further embodiment, the isolated nucleic acid further comprises athird nucleic acid that encodes an NAD synthetase protein selected fromthe group consisting of SEQ ID NO:10, 11, and 12. In another embodiment,the third nucleic acid consists of a NAD synthetase coding sequenceaccording to SEQ ID NO:13, 14, or 15. In another embodiment, theisolated nucleic acids of the invention are provided in a vector forreplication and expression.

In another aspect, the present invention provides recombinant host cellscomprising isolated nucleic acids or expression vectors according to theinvention. Such host cells can be used, for example, to produce largeamounts of the isolated nucleic acids of the invention, of to carry outthe methods of the invention. In one embodiment, the host cell is acyanobacterial host cell; in another embodiment, the recombinant hostcell is a bacterial host cell. In a further embodiment, the recombinantcyanobacterial host cell is selected from the group consisting ofSynechocystis, Arthrospira maxima, Synechococcus, Trichodesmium; andCrocosphaera. In another embodiment, the recombinant cyanobacterial hostcell is a Synechocystis PCC 6803 cell. In a further embodiment, therecombinant nucleic acid is chromosomally integrated into thecyanobacterial genome. In various further embodiments, thecyanobacterial host cells have been recombinantly engineered to deletethe slr1125 gene; the cyanobacterial host cells have been geneticallyengineered to overexpress NAD synthetase and/or NAD+ kinase; thecyanobacterial host cells are deficient in cyanophycin production; thecyanobacterial host are deficient in expression of Slr1993; thecyanobacterial host cells are deficient in cyanophycinase expression,and the cyanobacterial host cells are recombinantly engineered to reduceor eliminate expression of one or more of Slr1994, Slr1829, and Slr1830.

In a further aspect, the present invention provides recombinantcyanobacterial host cell, comprising:

(a) a deficiency in Slr1125 expression; and

(b) one or more of the following recombinantly generated phenotypes:

-   -   (i) a deficiency in cyanophycin production;    -   (ii) a deficiency in poly-β-hydroxyalkanoate (PHA) production;    -   (iii) overexpression of NAD synthetase;    -   (iv) overexpression of NAD+ kinase;    -   (v) deficiency in cyanophycin synthetase expression;    -   (vi) deficiency in Slr1993 expression;    -   (vii) deficiency in cyanophycinase expression;    -   (viii) deficiency in PHB production;    -   (ix) deficiency in Slr 1994 expression;    -   (x) deficiency in Slr 1829 expression; and    -   (xi) deficiency in Slr 1830 expression.

Such host cells can be used, for example, to carry out the methods ofthe invention. In one embodiment, the recombinant cyanobacterial hostcell has been genetically engineered to reduce or eliminate Slr1125expression. In another embodiment, the cyanobacteria is selected fromthe group consisting of Synechocystis, Arthrospira maxima,Synechococcus, Trichodesmium; and Crocosphaera. In a further embodiment,the recombinant cyanobacterial host cell is a Synechocystis sp. PCC 6803cell.

These aspects and embodiments of the invention are described in moredetail below, each of which can be combined except where the context ofthe specification clearly indicates otherwise.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a flow chart for PHB biosynthesis in Synechocystis.

FIG. 2 is a schematic diagram of an exemplary recombinant nucleic acidconstruct that can be used, for example, to create a stable transfectedcyanobacterial strain for PHA production.

FIG. 3 is a schematic diagram of a recombinant nucleic acid that iseffective for creating a stable cyanophycin-producing cyanobacterialstrain.

FIG. 4 is a schematic diagram of a recombinant nucleic acid suitable forproduction of 3-hydroxybutyrate.

DETAILED DESCRIPTION OF THE INVENTION

Within this application, unless otherwise stated, the techniquesutilized may be found in any of several well-known references such as:Molecular Cloning: A Laboratory Manual (Sambrook, et al., 1989, ColdSpring Harbor Laboratory Press), Gene Expression Technology (Methods inEnzymology, Vol. 185, edited by D. Goeddel, 1991. Academic Press, SanDiego, Calif.), “Guide to Protein Purification” in Methods in Enzymology(M. P. Deutshcer, ed., (1990) Academic Press, Inc.); PCR Protocols: AGuide to Methods and Applications (Innis, et al. 1990. Academic Press,San Diego, Calif.), Culture of Animal Cells: A Manual of BasicTechnique, 2^(nd) Ed. (R. I. Freshney. 1987. Liss, Inc. New York, N.Y.),and Gene Transfer and Expression Protocols, pp. 109-128, ed. E. J.Murray, The Humana Press Inc., Clifton, N.J.)

In one aspect, the present invention provides recombinant nucleic acids,comprising:

(a) a first nucleic acid comprising an inducible cyanobacterialpromoter; and

(b) a second nucleic acid operably linked to the first nucleic acid,wherein the second nucleic acid encodes an inhibitory nucleic acidcomplementary to a target nucleic acid sequence that encodes an aminoacid sequence of one or more polypeptides selected from the groupconsisting of SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, and SEQ ID NO:8.

The recombinant nucleic acids of this first aspect of the invention canbe used, for example, as constructs for producing recombinantcyanobacteria to control Slr1125 (or orthologue thereof) production. TheSlr1125 protein is a carotenoid glycosyl transferase involved in thebiosynthesis of myxoxanthophyll and the recombinant nucleic acids of theinvention can be used, for example, to produce bioplastics (such aspolyhydroxyalkanoates (“PHA”), which include, for example, PHBs asdiscussed below) and cyanophycin in larger quantity in cyanobacteriathan previously possible, based at least in part on the induction ofcell conversion into granule formation and biopolymer production bySlr1125 down-regulation, due to interruption of the carotenoidbiosynthesis/degradation pathway.

SEQ ID NO:2 is the amino acid sequence of Synechocystis sp. PCC 6803Slr1125. The filamentous cyanobacterium Trichodesmium erythraeum IMS 101has an Slr1125 orthologue (SEQ ID NO:4), with 55% identity at the aminoacid level, while the Crocosphaera watsonii WH 8501 (previously known asSynechocystis sp. WH 8501) Slr1125 apparently has been split up into twoopen reading frames (ZP_(—)00177831 (SEQ ID NO:6) and ZP_(—)00174102(SEQ ID NO:8)).

Thus, the recombinant nucleic acids incorporating a second nucleic acidencoding an inhibitory nucleic acid complementary to a nucleic acidsequence encoding one or more of the Slr1125 orthologues can also beused to produce bioplastics in larger quantity in cyanobacteria thanpreviously possible.

As used herein, “recombinant nucleic acids” are those that have beenremoved from their normal surrounding nucleic acid sequences in thegenome or in cDNA sequences. Such recombinant nucleic acid sequences maycomprise additional sequences useful for promoting expression of theinhibitory nucleic acid, or any other useful signals.

The term “operably linked” refers to the association of the first andsecond nucleic acids in a single recombinant nucleic acid so that theexpression of the second nucleic acid is activated by the first nucleicacid. Thus, the first nucleic acid is operably linked to the secondnucleic acid when it is capable of affecting the expression of thesecond nucleic acid.

As used herein, the term “expression” refers to the transcription ofsense (mRNA) or antisense RNA derived from the nucleic acid fragment ofthe invention. Expression may also refer to translation of mRNA into apolypeptide.

The term “inhibitory nucleic acid” means any type of nucleic acid thatcould inhibit expression (transcription or translation), or accumulationof the expression product (RNA or protein), of its target nucleic acidsequence. Such inhibitory nucleic acids include, but are not limited to,antisense nucleic acids, small interfering nucleic acids, ribozymes, andaptamers that bind the target nucleic acid.

“Antisense RNA” refers to a RNA transcript that is complementary to allor part of a target primary transcript or mRNA and that blocks theexpression of a target gene (U.S. Pat. No. 5,107,065). Thecomplementarity of an antisense RNA may be with any part of the specificgene transcript, i.e., at the 5′ non-coding sequence, 3′ non-codingsequence, introns, or the coding sequence. “Functional RNA” refers toantisense RNA, ribozyme RNA, or other RNA that is not translated yet hasan effect on cellular processes. “Sense” RNA refers to RNA transcriptthat includes the mRNA and so can be translated into protein by thecell.

“Antisense inhibition” refers to the production of antisense RNAtranscripts capable of suppressing the expression of the target protein.“Co-suppression” refers to the production of sense RNA transcriptscapable of suppressing the expression of identical or substantiallysimilar foreign or endogenous genes (U.S. Pat. No. 5,231,020).

The term “complementary” is used to describe the relationship betweennucleotide bases that are capable to hybridizing to one another. Forexample, with respect to DNA, adenosine is complementary to thymine andcytosine is complementary to guanine. The inhibitory nucleic acid iscomplementary to the target nucleic acid over a region large enough toinhibit expression or accumulation of the target nucleic acid expressionproduct. In one embodiment, the inhibitory nucleic acid is complementaryto at least 20 contiguous nucleotides of the target nucleic acid; invarious further embodiments, the inhibitory nucleic acid iscomplementary to at least 30, 50, 100, 250, or 500 contiguousnucleotides of the target nucleic acid, or is complementary to theentire nucleic acid sequence of the target nucleic acid.

“Promoter” refers to a DNA sequence capable of controlling theexpression of the second nucleic acid. In general, the second nucleicacid is located 3′ to the inducible promoter, although any arrangementthat permits an operable linkage of the first and second nucleic acidscan be used. “Inducible” means that the promoter does not constitutivelyactivate expression of the second nucleic acid, but allows for regulatedexpression. The inducible promoters may be derived in their entiretyfrom a native gene, or be composed of different elements derived fromdifferent promoters found in nature, or even comprise synthetic DNAsegments. It is understood that since in most cases the exact boundariesof regulatory sequences have not been completely defined, DNA fragmentsof different lengths may have identical promoter activity.

The term “Cyanobacterial promoter” means that the promoter is capable ofdirecting expression of the second nucleic acid in a cyanobacteria (forexample, Synechocystis, Trichodesmium, and Crocosphaera), and is notlimited to promoters derived from cyanobacteria.

In one embodiment of this first aspect, the target nucleic acid sequencecomprises or consists of a nucleic acid selected from SEQ ID NO:1, SEQID NO:3, SEQ ID NO:5, and SEQ ID NO:7, which are the coding DNA for SEQID NOS: 2, 4, 6, and 8, respectively.

As will be understood by those of skill in the art, the inhibitorynucleic acid can be used in different cyanobacterial species, so long asit has sufficient identity with the target nucleic acid sequence. In apreferred embodiment, the strain from which the inhibitory nucleic acidis derived is used. In prokaryotes, the gene is translated during itstranscription, so the RNA is usually connected from one side with thetranscription enzymes and the other end has the ribosome attached to itfor translation. Therefore, in further embodiments, a full lengthantisense-RNA molecule is used so it can bind to whatever exposedsegment of the RNA molecule during the transcription-translationprocess, in addition to full binding to the free RNA molecules. Theseembodiments also ensure the maximum specificity of inhibition.

The first nucleic acid comprises or consists of an induciblecyanobacterial promoter. As used herein, “inducible” means that theexpression of the inhibitory nucleic acid from the promoter can beregulated and thus increased or decreased as desired by application ofan appropriate stimulus to cells in which the promoter is functional,Any inducible promoter capable of replicating in cyanobacteria can beused, while those inducible in cyanobacteria selected from the groupconsisting of Synechocystis, Arthrospira maxima Trichodesmium, andCrocosphaera are preferred. In one embodiment, the induciblecyanobacterial promoter comprises a plastocyanin promoter (inducible bycopper), according to SEQ ID NO:9, or a functional equivalent thereof.In other embodiments, the inducible cyanobacterial promoter comprises orconsists of an inducible promoter as disclosed in US20040157331 orUS20020164706.

The recombinant nucleic acids of this aspect of the invention cancomprise further functional components as desired for a givenapplication. For example, the constructs can comprise one or morefurther nucleic acids that encode expression products of interest; suchfurther nucleic acids can be operably linked to the inducible promoter,or can be operably linked to one or more further promoters present inthe recombinant nucleic acid. In one such embodiment, the recombinantnucleic acids further comprise a third nucleic acid that encodes an NAD⁺synthetase protein (Slr1691) that comprises or consists of the aminoacid sequence of SEQ ID NO:10 (Synechocystis), 11 (Crocosphaera WatsoniiWH 8501), or 12 Trichodesmium Erythraeum IMS101). In a furtherembodiment of this first aspect of the invention, the third nucleic acidcomprises or consists of a NAD synthetase coding sequence according toSEQ ID NO:13 (Synechocystis), 14 (Crocosphaera Watsonii WH 8501), or 15(Trichodesmium Erythraeum IMS101).

In another embodiment of this first aspect of the invention, therecombinant nucleic acids further comprise a fourth nucleic acid thatencodes Sll1415, the putative NAD+-kinase, which comprises or consist ofthe amino acid sequence of SEQ ID NO:16 (Synechocystis sp. PCC 6803), 18Crocosphaera watsonii WH 8501), or 20 (Trichodesmium erythraeum IMS101),together with slr1691. In a further embodiment, the fourth nucleic acidcomprises or consists of a NAD+-kinase coding sequence according to SEQID NO:17 (Synechocystis sp. PCC 6803)), 19 Crocosphaera watsonii WH8501)), or 21 (Trichodesmium erythraeum IMS101).

PHA biosynthesis requires NADPH as a cofactor; therefore increasing NADbiosynthesis could enhance PHA production. Thus, the present inventionprovides cyanobacterial recombinants in which a copy of the NADsynthetase and/or the NAD+-kinase, can be introduced in front of theinducible promoter (such as the copper-controlled promoter), to overexpress NAD synthetase and/or the NAD+-kinase in coordination with theinduction of PHA biosynthesis, thereby increase the availability of thecofactor required for PHA biosynthesis.

The nucleic acids of the first aspect of the invention can furthercomprise “recombination sequences” for promoting double homologousrecombination in a cyanobacterial genome. As used herein, “DoubleHomologous recombination” means the exchange of DNA fragments betweentwo DNA molecules at two sites of identical nucleotide sequences. Thus,the “recombination sequences” comprise two nucleic acids that flank theregions desired to be recombined into the genome, wherein therecombination sequences are identical to sequences in the cyanobacterialgenome that are targeted for insertion of the recombinant nucleic acidsof the invention. See, for example, Mes and Stal, Gene. 2005 Feb. 14;346:163-71; and Mes and Doeleman, J Bacteriol. 2006 October;188(20):7176-85. In one embodiment, the region of the cyanobacterialgenome target for insertion can be a non-protein coding region; in otherembodiments, the targeted region of the cyanobacterial genome can be aprotein-encoding gene to be disrupted, thus providing the ability togenerate mutant cyanobacteria that cannot express the disruptedprotein-encoding gene, and which also express the recombinant nucleicacids of the invention. Further examples of these embodiments areprovided below.

The recombinant sequences of any of the embodiments of this first aspectcan further comprise sequences to promote replication in an organism ofchoice. Such sequences are well known in the art. For example,commercially available vectors (plasmid or viral) can be used with suchreplication capabilities, and the recombinant nucleic acids of theinvention can be cloned into the vector. Such replication competentvectors are useful, for example, to produce large quantities of therecombinant nucleic acids of the invention. The organism of choice canbe any organism in which replication of the recombinant nucleic acidswould be useful, including but not limited to E. coli.

The recombinant nucleic acids of the first aspect of the invention, andvectors comprising the recombinant nucleic acids of the first aspect ofthe invention, may further comprise nucleic acid sequences encoding aselectable marker to, for example, facilitate selection of host cellsexpressing the vector. The recombinant nucleic acids and vectors maycontain other promoter sequences and other encoded nucleic acids orpolypeptides, as discussed in more detail below, as well as relevantcontrol signals (ie, leader, transcriptional and translational stopsignals), and polylinkers for introducing specific restriction sitesfacilitating ligation in specific regions of the recombinant nucleicacids.

These embodiments of the first aspect of the invention can be combinedexcept where the context of the specification clearly indicatesotherwise.

In a second aspect, the present invention provides recombinant hostcells that (a) possess chromosomally integrated recombinant nucleicacids of the first aspect of the invention; and/or (b) are transfectedwith replication competent vectors comprising the recombinant nucleicacids of the first aspect of the invention. Such recombinant host cellscan be either prokaryotic or eukaryotic, with prokaryotic host cellspreferred. For example, the recombinant host cells transfected withrecombinant expression vectors constructed to permit expression in, forexample, E. coli, can be used for production of large quantities of therecombinant expression vectors and the recombinant nucleic acids of theinvention. Double homologous recombination is discussed above.Recombinant cyanobacterial host cells including, but not limited to,cyanobacteria selected from the group consisting of Chlorococcales(including Synechocystis and Synechococcus, with Synechocystis sp. PCC6803 and Synechococcus MA19 being preferred), Trichodesmium; andCrocosphaera, and specific strains disclosed in the Examples below, canbe used, for example, to produce large quantities of bioplastics, asdiscussed in more detail below. Transfection of expression vectors intoprokaryotic and eukaryotic cells can be accomplished via any techniqueknown in the art, including but not limited to standard bacterialtransformations, calcium phosphate co-precipitation, electroporation, orliposome mediated-, DEAE dextran mediated-, polycationic mediated-, orviral mediated transfection. (See, for example, Molecular Cloning: ALaboratory Manual (Sambrook, et al., 1989, Cold Spring Harbor LaboratoryPress; Culture of Animal Cells: A Manual of Basic Technique, 2^(nd) Ed.(R. I. Freshney. 1987. Liss, Inc. New York, N.Y.). Double homologousrecombination for producing recombinant cyanobacterial host cells isdiscussed above; see also Koksharova and Wolk, Appl MicrobiolBiotechnol. 2002 February; 58(2):123-37; and Golden, Methods Enzymol.1988; 167:714-27.

Recombinant cyanobacteria of the second aspect of the invention producelarge amounts of PHA and cyanophycin. In some cases, it may be desirableto produce large amounts of only one of these products to, for example,facilitate isolation of the product of interest. This can beaccomplished by further modifying the recombinant cyanobacteria of thesecond aspect of the invention to produce only one of these two majorproducts. Thus, in various further embodiments of any of the aboveembodiments, the recombinant cyanobacterial cells of the second aspectof the invention may further be deficient in one of:

-   -   (a) Cyanophycin expression; or    -   (b) poly-β-hydroxyalkanoate (PHA) expression.

Thus, in one set of further embodiments of the second aspect of theinvention, a recombinant cyanobacterial host cell according to theinvention is further deficient in expression of cyanophycin. In analternative set of further embodiments of the second aspect of theinvention, any of the recombinant host cells are further deficient inPHA expression. As used herein, “PHA” (also referred to herein as a“bioplastic”, which is a polymer of biological origin) includes any PHAin the cyanobacteria being manipulated, including but not limited to3-hydroxybutyryl-CoA, and poly(3-hydroxybutyrate) (“PHB”).

Any mechanism for creating the recited deficiency can be used, includingbut not limited to gene knockouts using double homologous recombinationand the construction of recombinant nucleic acids with a promoteroperably linked to an inhibitory nucleic acid that is complementary tothe expression product of a gene involved in cyanophycin expression(including but not limited to cyanophycin synthetase) or PHA expression(including but not limited to PHA synthetase); exemplary genes arediscussed below. If inhibitory nucleic acids are used, the operablylinked promoter can be a constitutive or inducible promoter; in eithercase the recombinant nucleic acid can be linked in a single constructwith the recombinant nucleic acids of the first aspect of the invention,or can be constructed as a recombinant nucleic acid separate from therecombinant nucleic acids of the first aspect of the invention.

In one embodiment, recombinant host cells of the second aspect of theinvention are deficient in cyanophycin expression; this strain isparticularly useful for PHA production. In another embodiment, thecyanophycin expression deficiency results from deletion of thecyanophycin synthetase gene from Synechocystis (SEQ ID NO:22) in thecyanobacteria. Examples of these embodiments are provided below.

Alternatively, the recombinant host cell of the second aspect of theinvention may further comprise an expression vector comprising a nucleicacid construct comprising a promoter sequence operatively linked to anucleic acid encoding an inhibitory nucleic acid complementary to atarget nucleic acid sequence that encodes an amino acid sequence ofSynechocystis cyanophycin synthetase (SEQ ID NO:23) (Slr2002). In afurther embodiment, the inhibitory nucleic acid is an antisensetranscript that comprises at least 20 contiguous nucleotides of thenucleic acid sequence of SEQ ID NO:22 (slr2002). In various furtherembodiments, the antisense transcript comprises at least a contiguous30, 50, 100, 250, 500, or the entire nucleic acid sequence of SEQ IDNO:22. In a preferred embodiment, the nucleic acid encoding theantisense transcript is operably linked to the cyanobacterial induciblepromoter.

In an alternative embodiment, the recombinant cyanobacterial cells ofthe second aspect of the invention are deficient in PHA expression,wherein the PHA expression deficiency results from deletion of theslr1993 gene (SEQ ID NO:24; from Synechocystis). This embodiment isparticularly useful for cyanophycin production. An example of thisembodiment is provided below. Alternatively, the recombinant host cellmay further comprise an expression vector comprising a nucleic acidconstruct comprising a promoter sequence operatively linked to a nucleicacid encoding an inhibitory nucleic acid complementary to a targetnucleic acid sequence that encodes the amino acid sequence of SEQ IDNO:25 (Slr1993). In a further embodiment, the inhibitory nucleic acid isan antisense transcript that comprises at least 20 contiguousnucleotides of the nucleic acid sequence of SEQ ID NO:24. In variousfurther embodiments, the antisense transcript comprises at least acontiguous 30, 50, 100, 250, 500, or the entire nucleic acid sequence ofSEQ ID NO:24. In a preferred embodiment, the nucleic acid encoding theantisense transcript is operably linked to a cyanobacterial induciblepromoter, such as the plastocyanin promoter discussed above.

Host cells combining the slr1125 mutant and the PHA deficient mutantscan be used, for example, for production/isolation of cyanophycin, sincePHA will not be abundantly expressed. In a further embodiment, thesehost cells may further include a second inhibitory nucleic acid whoseexpression is under control of the inducible promoter, wherein thesecond inhibitory nucleic acid is complementary to a target nucleic acidthat encodes cyanophycinase (Slr2001; see SEQ ID NO:26 fromSynechocystis), which degrades cyanophycin granules. In this embodiment,it is preferred that the second inhibitory nucleic acid targetingcyanophycinase and the inhibitory nucleic acid targeting slr1125 areboth under control of the same inducible promoter. The second inhibitorynucleic acid may be an antisense transcript that comprises at least 20contiguous nucleotides of the nucleic acid sequence of SEQ ID NO:27. Invarious further embodiments, the antisense transcript comprises at leasta contiguous 30, 50, 100, 250, 500, or the entire nucleic acid sequenceof SEQ ID NO:27. In an alternative embodiment, the cyanophycinasedeficiency results from deletion of the slr2001 gene (SEQ ID NO:27), ororthologue thereof.

PHB pathway in Synechocystis. Polyhydroxybutyrates (PHB), areintracellular reserve materials produced by a large number of bacteriaincluding cyanobacteria. In Synechocystis, three enzymes are involved inthe conversion of acetyl-CoA to PHB: beta ketothiolase (Slr1993),acetoacetyl-CoA reductase (Slr1994) and PHB polymerase (Slr1829 andSlr1830; these two ORFs encode two polypeptides which form the PHBheterodimer; absence of one or both is sufficient to completelyeliminate PHB polymerase activity). Two acetyl-CoA groups are condensedby beta-ketothiolase to form acetoacetyl-CoA. The acetoacetyl-CoA isthen reduced by an NADP-specific reductase to formD(−)-beta-hydroxybutyryl-CoA, the substrate for PHB polymerase.

In further embodiments, the recombinant cyanobacteria of the secondaspect of the invention can be rendered deficient for expression ofother PHA (such as PHB) biosynthesis pathway gene(s), resulting in adesired PHA pathway end product. These embodiments can preferably becombined with embodiments in which cyanophycin expression is inhibited,thus resulting in recombinant cyanobacteria that produce a desired PHA.A flow chart for PHB biosynthesis in Synechocystis is provided in FIG.1.

Thus, in various further embodiments, the recombinant cyanobacteria ofthe second aspect of the invention are further rendered deficient inexpression of one or more of:

Slr1994 (SEQ ID NO:28);

Slr1829 (SEQ ID NO:29); and

Slr1830 (SEQ ID NO:30). (Taroncher-Oldenburg et al., Appl EnvironMicrobiol. 2000 October; 66(10):4440-8; Hein et al., Arch Microbiol.1998 September; 170(3):162-70)

Those cells rendered deficient in slr1994 expression can be used, forexample, to produce acetoacetyl-CoA, which is useful, in one example,for feed stock for other bacteria to produce other desired chemicals;those rendered deficient in one or both of slr1829 and slr1830 can beused, for example, to produce poly(3-hydroxybutyryl-CoA), which can beused to produce 3-hydroxybutyryl-CoA and or 3-hydroxybutyryl monomerwhich is valuable as feed stock for other bacteria or for direct use asa biofuel.

In one embodiment, the expression deficiency results from deletion ofthe relevant gene (SEQ ID NO:31, 32, and/or 33) in the cyanobacteria.Examples of this embodiment are provided below. Alternatively, therecombinant cyanobacteria of the second aspect of the invention mayfurther comprise an expression vector comprising a nucleic acidconstruct comprising a promoter sequence operatively linked to a nucleicacid encoding an inhibitory nucleic acid complementary to a targetnucleic acid sequence that encodes an amino acid sequence of one or moreof SEQ ID NO:28, SEQ ID NO:29, and SEQ ID NO:30. In a furtherembodiment, the inhibitory nucleic acid is an antisense transcript thatcomprises at least 20 contiguous nucleotides of the nucleic acidsequence of one or more of SEQ ID NO:31, SEQ ID NO:32, and SEQ ID NO:33.In various further embodiments, the antisense transcript comprises atleast a contiguous 30, 50, 100, 250, 500, or the entire nucleic acidsequence of SEQ ID NO:31, SEQ ID NO:32, and SEQ ID NO:33. In a preferredembodiment, the nucleic acid encoding the antisense transcript isoperably linked to a cyanobacterial inducible promoter, such as theplastocyanin promoter discussed above.

In an alternative embodiment, the recombinant cyanobacterial cells ofthe second aspect of the invention are deficient in PHA expression,wherein the PHA expression deficiency results from deletion of theslr1993 gene (SEQ ID NO:24), or orthologue thereof. An example of thisembodiment is provided below. Alternatively, the recombinant host cellmay further comprise an expression vector comprising a nucleic acidconstruct comprising a promoter sequence operatively linked to a nucleicacid encoding an inhibitory nucleic acid complementary to a targetnucleic acid sequence that encodes the amino acid sequence of SEQ IDNO:25. In a further embodiment, the inhibitory nucleic acid is anantisense transcript that comprises at least 20 contiguous nucleotidesof the nucleic acid sequence of SEQ ID NO:24. In various furtherembodiments, the antisense transcript comprises at least a contiguous30, 50, 100, 250, 500, or the entire nucleic acid sequence of SEQ IDNO:24. In a preferred embodiment, the nucleic acid encoding theantisense transcript is operably linked to a cyanobacterial induciblepromoter, such as the plastocyanin promoter discussed above.

The following are specific examples of recombinant nucleic acidconstructs that fall within the scope of the present invention, togetherwith specific uses for such constructs.

FIG. 2 provides a schematic diagram of an exemplary construct that canbe used, for example, to create a stable transfected cyanobacterialstrain for PHA production. The construct can be cloned into any standardvector for purposes of propagation in, for example, E. coli. Anyantibiotic resistance marker suitable for use with the host cells of theinvention can be used, including but not limited to chloramphenicol.

Each box represents a segment of DNA. The “N-terminal” and “C-terminal”of slr2002 is an abbreviation for the upstream and downstream sites fordouble homologous recombination with the genomic slr2002 gene. Slr2002is the cyanophycin synthetase gene discussed above (SEQ ID NO:22). Aswill be understood by those of skill in the art, the use of 600 by ofthe 5′ sequence of slr2002 (SEQ ID NO:34) or 3′ sequence of slr2002 (SEQID NO:35) is exemplary. In various embodiments, 200 or more nucleotidescan be used, with a larger number of nucleotides preferred.

Inserting the nucleic acid construct comprising a nucleic acid encodingan antisense-slr1125 operably linked to the copper-controlled petEpromoter inside the slr2002 homologous recombination sequences andtransfecting a cyanobacterium with the construct via double homologousrecombination results in recombinant cyanobacteria that produce largeamounts of PHA in the presence of copper, but are unable to synthesizecyanophycin granules, thus facilitating exclusive production andpurification of PHA from the host cells without interference fromcyanophycin.

FIG. 3 provides a schematic of a recombinant nucleic acid according tothe invention that is effective for creating a stablecyanophycin-producing strain for pure cyanophycin production. In thiscase, the recombination sequences are derived from slr1993 (PHA-specificbeta-ketothiolase gene) (SEQ ID NO:24), so a recombinant cyanobacteriumtransfected with this construct via double homologous recombination isdeleted for this gene and does not synthesize PHA. The construct furthercomprises nucleic acids encoding antisense-slr1125 and also antisenseslr2001, the gene for cyanophycinase, which degrades cyanophycingranules (see above), each operably linked to the copper-controlled petEpromoter.

Thus, exposure of the cells to copper will result in antisenseexpression from the construct, which will down regulate cyanophycinase,while antisense-slr1125 will induce the cyanophycin granule formation inthe absence of PHB biosynthesis and cyanophycin degradation.

FIG. 4 shows a schematic diagram of a recombinant nucleic acid of theinvention suitable for production of 3-hydroxybutyrate. In this case,the recombination sequences are derived from slr1829(poly(3-hydroxyalkanoate synthase gene) (SEQ ID NO:32)), so arecombinant cyanobacterium transfected with this construct via doublehomologous recombination is deleted for this gene and does notsynthesize PHB.

The construct further comprises nucleic acids encoding antisense-slr1125and also antisense slr2002, the gene for cyanophycin synthetase (SEQ IDNO: 22), each operably linked to the copper-controlled petE promoter.Thus, exposure of the cells to copper will result in antisenseexpression from the construct, which will down regulate cyanophycinexpression, while antisense-slr1125 will induce the accumulation of3-hydroxybutyryl acid as a monomer without polymerization due to theabsence of a functional slr1829 gene.

These embodiments of the second aspect of the invention can be combinedas desired, as well as combined with various embodiments of the firstaspect of the invention except where the context of the specificationclearly indicates otherwise.

In a third aspect, the present invention provides methods for producingbiomaterials, comprising:

(a) culturing cyanobacterial host cells that are deficient in Slr1125expression;

(b) harvesting the cyanobacterial host cells; and

(c) preparing biomaterials from the harvested cyanobacterial host cells.

The methods of the invention can be used, for example, to producequantities of biomaterials not previously possible using knowncyanobacterial host cells. The cyanobacterial host cells may benaturally deficient in Slr1125 expression, or may be geneticallyengineered to reduce or eliminate Slr1125 expression. In one embodiment,such engineering comprises deleting the slr1125 gene. In anotherembodiment, such engineering comprises use of host cells as disclosedabove, in which slr1125 is under control of an inducible promoter, suchthat expression of Slr1125 can be controlled as desired. For example,antisense technology can be achieved using the native copper-controlledplastocyanin promoter with slr1125 in the antisense direction behind it,as discussed above, permitting down-regulating the expression of Slr1125by adding μM amounts of copper to the medium. This protocol provides adirect and cheap way of controlling slr1125 gene expression.

The inventors have discovered that cyanobacteria deficient in Slr1125expression are capable of producing large amounts of granules andreleasing their granules content, in which a mixture of PHA andcyanophycin are the predominant products, facilitating production ofmuch large amounts of these products than was possible in the art.

All of the embodiments of the recombinant nucleic acids and host cellsof the first and second aspects of the invention are equally applicablefor use in this third aspect of the invention. As disclosed above, thevarious embodiments were all based on combinations with the inducibleslr1125 inhibitor construct; in this third aspect, all of the variousembodiments above are equally compatible, alone or in combination, foruse with the slr1125 deletion mutant.

Thus, in one exemplary embodiment, the biomaterials produced comprisebiomaterials selected from the group consisting of polyhydroxyalkanoates(PHA) and cyanophycin. In another embodiment, the cyanobacterial hostcells are selected from the group consisting of Synechocystis,Arthrospira maxima, Synechococcus, Trichodesmium, and Crocosphaera. In afurther embodiment, the cyanobacterial host cells are Synechocystis PCC6803 cells. In another embodiment, the cyanobacterial host cells havebeen genetically engineered to overexpress NAD synthetase and/or NAD+kinase, wherein the culturing comprises culturing the recombinantcyanobacterial host cells under conditions suitable to overexpress NADsynthetase and/or NAD+ kinase.

In a further embodiment, the method comprises preparation of PHA,wherein the cyanobacterial host cells are deficient in cyanophycinproduction, for example, by recombinantly engineering the cyanobacterialhost cells to reduce or eliminate expression of cyanophycin synthetasein the cyanobacterial host cells. In another embodiment, the methodcomprises preparation of cyanophycin, wherein the cyanobacterial hostcells are deficient in PHA production, for example, by recombinantlyengineering the cyanobacterial host cells to reduce or eliminateexpression of Slr1993 in the cyanobacterial host cells. In anotherembodiment, the cyanobacterial host cells are deficient incyanophycinase expression.

In another embodiment, the method comprises preparation of PHA, whereinthe cyanobacterial host cells are deficient in production ofpolyhydroxybutyrates (PHB), for example, by recombinantly engineeringthe cyanobacterial host cells to reduce or eliminate expression of oneor more of Slr1994, Slr1829, and Slr1830. In one embodiment, thecyanobacterial host cells have been genetically engineered to reduce oreliminate expression of Slr1994, and wherein the method comprisesproduction of acetoacetyl-CoA. In another embodiment, the cyanobacterialhost cells have been genetically engineered to reduce or eliminateexpression of one or both of Slr1829 and Slr1830, and wherein the methodcomprises production of poly(3-hydroxybutyryl-CoA).

Preparation of nucleic acid constructs and recombinant cyanobacterialhost cells according to these various embodiments are described indetail above.

The culture conditions used can be any that are suitable for productionof the biomaterials of interest. Exemplary culture conditions forslr1125 deletion mutants are provided in the examples below. A majoradvantage in using cyanobacteria for bioplastics production is thatsolar energy provides the energy input. In one example, cyanobacteriacan be grown at between 25° C. and 34° C. (for example, Synechocystissp. PCC 6803 grows between 25° C.-34° C. with optimum temperature (30°C.)), with shaking in a media such as buffered BG-11 medium (40) in thepresence of appropriate light conditions, such as between 50 to 200 μmolof photons m⁻²s⁻¹, where 50 is low light and 200 is high light. As willbe understood by those of skill in the art, large scale production cellscan be adapted to different light regimes according to location and thebioreactor specifications, for example, up to 600 μmol of photons m⁻²s⁻¹which is approximately equivalent to a bright sunny day by taking intoaccount the self shading effect of the cells. Light conditions can varyas appropriate for a given purpose, and can be continuous or periodic;for large scale and outdoor cultivation, light/dark cycling is preferredto minimize the cost and avoid extra cost from artificial lighting.Under such conditions, large scale cyanobacterial growth can result inhigh density cultures.

In one embodiment, granulation is induced during cell growth bysubstituting ammonia for nitrates as the nitrogen source in the growthmedium. Cyanobacteria do not fix nitrogen and thus a nitrogen source isneeded in the growth medium; using ammonia as the nitrogen sourceeliminates the need for cyanobacterial conversion of nitrates toammonia, limits consumption of NADPH reducing power, and permittingincreased NADPH reserves in the cells for granulation and biomaterialsbiosynthesis during the induction phase. In one embodiment, the amountof ammonia is approximately equimolar to the amount of nitrates in thestandard growth medium; in another embodiment, the amount of ammoniaranges from 0.75 g/L to 1.5 g/L; in another embodiment, it ranges from0.75 g/L to 1.25 g/L; in another embodiment, it ranges from 0.75 g/L to1.0 g/L. In a further embodiment of any of these granulationembodiments, cells can be grown to maximal density, and granulationinduced to maximize production of biomaterials of interest, such as PHB,cyanophycin and 3-hydroxybutyrate. In a further embodiment, thecyanobacterial cells have been recombinantly engineered to induciblydown-regulate expression of the slr1125 gene, such as by inclusion of acopper-inducible promoter, as disclosed above. In a further embodiment,NAD synthetase and/or NAD kinase can be overexpressed in conjunctionwith slr1125 down-regulation or deletion. In one non-limiting example,Synechocystis sp. PCC 6803 has a doubling time of 8-10 hours. Therefore,biomass of 4-5 OD₇₃₀/Liter can be divided into two halves: one can befurther grown to allow a continuous supply of cell-biomass, while theother half can be used to stimulate granule production as discussedabove.

In a further embodiment, granulation can be induced by including aninhibitor of lycopene cyclase in the growth medium; examples of suchinhibitors include, but are not limited to, nicotinic acid (5-50 uM),chlorophenoxytriethylamine (COPTA), 2-(4-chlorophenylthio)-triethylamine(CAPT), 2-(3,4-dichlorophen-oxy)-triethylamine (DCPTA),2-(3,5-dimethylphenoxy)-triethylamine (DMPTA),2-(4-methyl-phenoxy)-triethylamine (MPTA), aminotriazole, azasqualene,dodecyltrimethylammonium, N,N-dimethyldodecylamine, imidazole, piperonylbutoxide, piperidine, triethylamine, and pyridine. The use of suchinhibitors enhances granule formation and reduces granulation time afterthe cell culture reaches its maximum density. In one embodiment, theculture media includes nitrates as a nitrogen source; in anotherembodiment, ammonia is provided as a nitrogen source. Any of the slr1125constructs can be used with the deletion mutant being preferred forembodiments employing carotenoid biosynthesis inhibitors (e.g.desaturases and cyclases).

Carotenoid is a group of C₄₀ hydrocarbons that is synthesized frompolymerization of Isopentenyl pyrophosphate (IPP) with its isomer,dimethylallyl pyrophosphate (DMPP), both are C₅ hydrocarbon molecules,through a sequential steps until it form phytoene (C₄₀ molecules). Thismolecule is the first committed carotenoid molecule synthesized in thecarotenoid biosynthesis pathway of the cyanobacterium Synechocystis sp.PCC 6803. Introduction of four double bounds to the phytoene moleculeproduces a desaturated C₄₀ lycopene by the action of two carotenedesaturases enzymes (phytoene desaturase and zeta-carotene desaturase).Lycopene is further cyclized by lycopene cyclase to produce monocyclic(Gamma-carotenel) or dicyclic carotenes (Beta-carotene). In the case ofmyxoxanthophyll additional enzymes are required to further modifymonocyclic carotenoid molecules to produce the glycosylated molecule(sll0254, slr1293 and slr1125), the product of these genes are majorenzymes required for the final formation of myxoxanthophyll carotenoidglycoside. The final major carotenoids are further processed to smallercarotenoid products (e.g. retinal group). The inhibitors listed belowinhibit one or more of the carotenoid biosynthesis/degradation enzymesand block the biosynthesis of myxoxanthophyll. Therefore, using one ormore of these inhibitors with combinations of the host cells of theinvention provides additional control to produce and increasebiomaterials (such as PHB and cyanophycin) and reduces the granulationtime needed for full conversion of cell to granules. In one embodiment,one or more of the inhibitor are used for large scale production of PHBand cyanophycin from cyanobacteria to further improve both quantity andthe quality of the final product and minimize the cost. Table 1 providespreferred concentration ranges in culture media for the inhibitors.

TABLE 1 Preferred concentration Inhibitors range  1- COPTA,chlorophenoxytriethylamine, 5 ug/L-25 ugl/L  2- CAPT(2-(4-chlorophenylthio)- 5 ug/L-25 ugl/L triethylamine);  3- DCPTA,2-(3,4-dichlorophen-oxy)- 25 ug/L-50 ugl/L  triethylamine  4- DMPTA,2-(3,5-dimethylphenoxy)- 25 ug/L-50 ugl/L  triethylamine  5- MPTA,2-(4-methyl-phenoxy)- 15 ug/L-50 ugl/L  triethylamine  6- Aminotriazole0.5 mg/L-1.5 mgl/L   7- Azasqualene 5 ug/L-15 ugl/L  8- Azasqualene 50ug/L-250 ugl/L  9- Dodecyltrimethylammonium 2 ug/L-25 ugl/L 10-N,N-Dimethyldodecylamine 25 ug/L-250 ugl/L 11- imidazole 250 ug/L-500ugl/L  12- piperonyl butoxide 5 ug/L-50 ugl/L 13- piperidine 50 ug/L-100ugl/L 14- triethylamine 50 ug/L-150 ugl/L 15- pyridine 100 ug/L-150ugl/L 

The dramatic change in availability of electrons induced by the variousconditions disclosed above, accumulation of NADPH, and change in lightdue to self shading effects greatly promote increased granule formationin the cyanobacterial host cells of the invention.

Similar culture conditions can be used for recombinant cyanobacteriathat carry an inducible promoter linked to an inhibitory nucleic acidwhose expression down-regulates expression of the open reading frame ofslr1125 (or orthologues thereof), except that appropriate conditions forinduction are used when appropriate. The relevant conditions under whichto reduce slr1125 expression will be dependent on the inducible promoterused, as well as other factors, including but not limited to thespecific cyanobacteria used, cyanobacterial concentration, media, pH,temperature, light exposure, etc. However, those of skill in the art candetermine the specific conditions to be used, in light of the teachingsherein. In one exemplary embodiment, the inducible promoter comprisesthe petE promoter (SEQ ID NO:9), and expression of the inhibitorynucleic acid is induced by the addition of μM amounts of copper to themedia. (See, for example, (Briggs, et al., 1990)) While those of skillin the art can determine an optimal concentration of copper, rangesbetween 2 and 10 μM have been used under laboratory conditions. In oneembodiment, an antisense slr1125 construct is downstream, and under thecontrol, of the petE promoter. Thus, adding μM amounts of copper to themedium will result in down-regulation of slr1125 expression, granuleproduction, and the ability to harvest the cells and prepare PHA andcyanophycin from the cells.

Harvesting of the cyanobacterial cells can be accomplished by anytechnique known to those of skill in the art, including but not limitedto centrifugation and filtration.

Similarly, methods for preparing biomaterials from the harvestedrecombinant cyanobacteria can be carried out by any means known in theart, such as those described in the examples below. In one non-limitingembodiment, PHA polyesters can be recovered and purified in a procedureconsisting of acidic non-PHA cell mass dissolution, pH adjustment (pH10), and final decolorization in a bleaching solution. The major productproduced by the recombinant cyanobacteria of the invention is a mixtureof PHA and cyanophycin. As noted above, in various embodiments, separatecyanobacterial strains (cyanohphycin-deficient and PHAsynthetase-deficient) are produced to discriminate between thebiosynthesis of these two polymers.

Cyanophycin, a copolymer of L-aspartic acid and L-arginine, is producedvia non-ribosomal polypeptide biosynthesis by the enzyme cyanophycinsynthetase. In a further embodiment, the isolated biomaterial comprisescyanophycin, which is then partially hydrolyzed using any suitablemethod, including but not limited to boiling at high pH, to producepolyaspartate, which is a biodegradable substitute for chemicallysynthesized polycarboxylate. The latter is an anionic polyelectrolyte,which can be used as a highly effective pigment dispersing agent for usein waterborne industrial, protective coatings, gloss dispersion paintsas well as printing inks. It is also used in pigment concentrates usedfor tinting paints, leather finishes, textiles, plastics, inks, etc. Itis used in conjunction with a wide variety of binders such as physicallydrying acrylic dispersions, air-drying alkyd emulsions,polyester-melamine, 2-pack epoxies, acrylates etc. Therefore, thisembodiment of the invention provides a very cost-effective way forcyanophycin (polyaspartate) production to replacetoxic-polycarboxylates, and which can also be used as energy and watersavers (ie: forming a thin film on water surface of lakes and pools toprevent water evaporation).

Thus, in various embodiments noted above, the recombinant cyanobacteriafor use in the third aspect of the invention may further be deficient incyanophycin expression or PHA expression, as disclosed above. Separationand purification of PHA polymers from non-PHA cell mass presents atechnical challenge due to the solid phase of both PHA granules andnon-PHA cell mass. The purity, yield, and molecular size are three majorfactors in PHA recovery. PHA polyesters (such as PHB) can be recoveredand purified in a procedure consisting of acidic non-PHA cell massdissolution, pH adjustment (pH 10), and final decolorization in ableaching solution. Thus, using cells that are deficient in cyanophycinexpression facilitates separation and purification of PHA produced bythe recombinant cyanobacteria of the invention. Similarly, using cellsthat are deficient in PHA synthetase expression facilitates separationand purification of the cyanophycin produced by the recombinantcyanobacteria of the invention. PHA biosynthesis requires NADPH as acofactor; therefore increasing NAD biosynthesis could enhance PHAproduction and reduce the time for full conversion to granules. Thus, asdiscussed above, the present invention provides cyanobacterialrecombinants in which a copy of the NAD(+) synthetase can be introducedin front of the copper-controlled promoter to over express incoordination with the induction of PHA biosynthesis, thereby increasingthe availability of the cofactor required for PHA biosynthesis.

In one non-limiting example, Synechocystis sp. PCC 6803 has a doublingtime of 8-10 hours. Therefore, biomass of 4 OD₇₃₀/Liter can be dividedinto two halves: one can be further grown to allow a continuous supplyof cell-biomass, while the other half can be used to granule productionphase. The continuous supply of the biomass of 4-5 OD₇₃₀/Liter of cellscan be achieved daily using sun light. For example: A plastic bag of 20cm×100 cm×250 cm (width×length×height) provides a 500 L which yieldapproximately 1.5 kg/bag/day biomass that converted to 0.75-1.0kg/bag/day PHA (50%) wt/wt dry biomass. The methods of the inventionachieve very high and pure yield that is approximately 80-90% wt/wt drybiomass that provides 1.2-1.35 kg/bag/day PHA, which represents anunprecedented yield for these biomaterials from biologicallyphotoautotrophic organisms to date.

In a fourth aspect, the present invention provides recombinantcyanobacterial host cells, comprising:

(a) a deficiency in Slr1125 expression; and

(b) one or more of the following recombinantly generated phenotypes:

-   -   (i) a deficiency in cyanophycin production;    -   (ii) a deficiency in poly-β-hydroxyalkanoate (PHA) production;    -   (iii) overexpression of NAD synthetase;    -   (iv) overexpression of NAD+ kinase;    -   (v) deficiency in cyanophycin synthetase expression;    -   (vi) deficiency in Slr1993 expression;    -   (vii) deficiency in cyanophycinase expression;    -   (viii) deficiency in PHB production;    -   (ix) deficiency in Slr 1994 expression;    -   (x) deficiency in Slr 1829 expression; and    -   (xi) deficiency in Slr 1830 expression.

The host cells of this aspect of the invention can be used, for example,to prepare large amounts of biomaterials according to the methods of theinvention disclosed above.

Embodiments for generating recombinant cyanobacterial host cells withany of the recited expression deficiencies or overexpression aredisclosed above and are equally applicable for use in this fourth aspectof the invention. In this aspect, the recombinant cyanobacterial hostcell has a deficiency in Slr1125 expression and at least one furtheraltered phenotype from the recited list, which increases the capacity ofthe recombinant to produce biomaterials, such as PHAs and cyanophycin.In one embodiment, the deficiency in Slr1125 expression may be based ona naturally occurring deficiency. In another embodiment, the host cellis engineered to cause the deficiency, such as by deletion of theslr1125 gene. In another embodiment, such engineering comprises use ofhost cells as disclosed above, in which slr1125 is under control of aninducible promoter, such that expression of Slr1125 can be controlled asdesired, and as disclosed in detail above.

The at least one further recombinant alteration in expression in thecyanobacterial host comprises one or more of the recited alterations,each of which is disclosed in detail above. In various furtherembodiments, the cyanobacteria is selected from the group consisting ofSynechocystis, Arthrospira maxima, Synechococcus, Trichodesmium; andCrocosphaera; in a further embodiment, the recombinant cyanobacterialhost cell is a Synechocystis PCC 6803 cell.

EXAMPLES

Cloning of slr1125 and construction of the pΔslr1125S plasmid—TheSynechocystis sp. PCC 6803 slr1125 gene and its flanking regions werecloned by polymerase chain reaction (PCR) based on the availableSynechocystis genomic sequence (CyanoBase; web site:kazusa.or.jp/cyano/cyano.html) (Kaneko et al.). The forward primer was5′ CTAGAAACGGGAATTCAAGCGGAAT 3′ (SEQ ID NO: 39) with an engineered EcoRI site (underlined) and corresponding to base number 85721-85745 inCyanoBase; the reverse primer was 5′ GTTTAATAGCATGCTTTGCCAGC 3′ (SEQ IDNO: 40) with an engineered Sph I restriction site (underlined) and asequence corresponding to CyanoBase bases 87845-87867 (base changes tointroduce restriction sites have been bolded). The PCR-amplifiedsequence corresponds to slr1125 with approximately 430-450 by flankingsequence on both sides of the ORF. A PCR product of the expected size(2.147 kb) was purified, restricted with EcoR I and Sph I (using theintroduced restriction sites in the primers) and cloned into pUC19creating pslr1125 construct. The slr1125 gene was deleted by restrictionat internal Sty I sites near the beginning and end of the slr1125 openreading frame and replacing the Sty I fragment (1.2 kb) by a 1.5 kbstreptomycin resistance cassette. This creates the pΔslr1125S construct,which was used for transformation of Synechocystis sp. PCC 6803, carriedout according to Vermaas et al. 1987. Transformants were propagated onBG-11/agar plates supplemented with 5 mM glucose and increasingconcentrations of up to 300 ug/ml of streptomycin dissolved in sterilewater. The segregation state of the transformants was monitored by PCRof transformant DNA using primers recognizing sequences upstream anddownstream of the slr1125-coding region. Synechocystis sp. PCC 6803genomic DNA used for PCR analysis of mutants was prepared as describedin He et al. The sequence of the cloned slr1125 ORF with flankingregions up and down stream was verified (SEQ ID NO:41).

Growth conditions. Synechocystis sp. strain PCC 6803 was cultivated on arotary shaker at 30° C. in BG-11 medium (40), buffered with 5 mM N-tris(hydroxymethyl) methyl-2-aminoethane sulfonic acid-NaOH (pH 8.2). Forgrowth on plates, 1.5% (wt/vol) Difco agar and 0.3% (wt/vol) sodiumthiosulfate were added. Flux densities of 40, and 100 μmol of photonsm⁻²s⁻¹ from cool-white fluorescent tubes were used for growth incontinuous light in liquid medium. The normal BG11 media described byRippka et al. 1979 contains nitrate as a source of nitrogen for thegrowth of Synechocystis strains; this medium composition provides cellpropagation to its maximum limit (3-5 OD₇₃₀).Granulation Conditions.

To start the granule induction phase, the cells were diluted to 0.75OD730 with BG11 medium containing an equimolar amount of ammonia (1 g/L)as a nitrogen source instead of nitrate; this strategy savesapproximately 40% of the reducing power of NADPH, which promotesincreased granule biosynthesis. Cells were cultures for an additional 48hours under the same culture conditions discussed above. Under theseculture conditions, little further cell growth occurred, as the growthconditions favored large scale granule production.

Extraction of PHB

One of the benefits of the current invention is that once granulation isinduced, PHB granules float on the media surface and can be collecteddirectly from the surface in the large scale. A one liter culture of0.75 OD₇₃₀ cells was collected by centrifugation to collect everythingin the media and precisely analyze the amount of PHB. The collectedgranules and cell materials were suspended in methanol (4° C.,overnight) for the removal of pigments. The pellet obtained aftercentrifugation was dried at 60° C. and PHB was extracted in hotchloroform followed by precipitation with cold diethyl ether. Theprecipitate was centrifuged at 11 000 g for 20 min, washed with acetoneand dissolved again in hot chloroform.

Spectrophotometric Measurement of PHB.

The spectrophotometric assay was performed as per Law and Slepecky(1961). The sample containing the polymer in chloroform was transferredto a clean test tube. The chloroform was evaporated and 10 ml ofconcentrated H₂SO₄ was added. The solution was heated in a water bathfor 20 min. After cooling and thorough mixing the absorbance of thesolution was measured at 235 nm against H₂SO₄ blank. To further confirmthe presence of PHB, absorption spectra (200-1000 nm) of the sample aswell as the standard (dl-β-hydroxybutyric acid, Sigma Chemical Co., USA)were compared by Spectrophotometer following acid digestion. Thesespectra were further compared with the spectrum of crotonic acid whichis the byproduct of acid hydrolysis of PHB and the compound that absorbat 235 nm in case of standard PHB or the PHB from the cell. A total of200 mg was collected from a 0.75 OD₇₃₀ culture flask of the slr1125deletion strain. The absorption at 235 nm of the extracted granules wascompared to standard curve generated by β-hydroxybutyric acid, SigmaChemical Co., USA. 105 mg PHB was measured out of 200 mg cell materialswhich approximately give 52% PHB/Dry weight of material collected.

References

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We claim:
 1. An isolated recombinant nucleic acid, comprising: (a) afirst nucleic acid which comprises an inducible cyanobacterial promoter;and (b) a second nucleic acid operably linked to the first nucleic acid,wherein the second nucleic acid comprises the full-length complement ofthe polynucleotide of SEQ ID NO:
 1. 2. The isolated nucleic acid ofclaim 1 wherein the inducible cyanobacterial promoter comprises SEQ IDNO:9.
 3. An expression vector comprising: (a) a first nucleic acid whichcomprises an inducible cyanobacterial promoter; and (b) a second nucleicacid operably linked to the first nucleic acid, wherein the secondnucleic acid comprises the full-length complement of the polynucleotideof SEQ ID NO:
 1. 4. A recombinant Synechocystis PCC 6803 host cell,wherein the host cell has been modified to introduce an inactivatinginsertion or deletion in an endogenous gene encoding the protein of SEQID NO:
 2. 5. A recombinant Synechocystis PCC 6803 host cell, wherein thehost cell comprises a recombinant nucleic acid that comprises: (a) afirst nucleic acid which comprises an inducible cyanobacterial promoter;and (b) a second nucleic acid operably linked to the first nucleic acid,wherein the second nucleic acid comprises the full-length complement ofthe polynucleotide of SEQ ID NO:
 1. 6. A method for producing apolyhydroxybutyrate (PHB), comprising: (a) culturing recombinantSynechocystis PCC 6803 host cells, wherein the host cells have beenmodified to introduce an inactivating insertion or deletion in anendogenous gene encoding the protein of SEQ ID NO: 2; (b) harvesting therecombinant Synechocystis PCC 6803 host cells; and (c) isolating the PHBfrom the recombinant Synechocystis PCC 6803 host cells.
 7. A method forproducing a PHB, comprising: (a) culturing recombinant Synechocystis PCC6803 host cells, wherein the host cells have been transformed with arecombinant nucleic acid, wherein said recombinant nucleic acidcomprises: (i) a first nucleic acid which comprises an induciblecyanobacterial promoter; and (ii) a second nucleic acid operably linkedto the first nucleic acid, wherein the second nucleic acid comprises thefull-length complement of the polynucleotide of SEQ ID NO: 1; (b)harvesting the recombinant Synechocystis PCC 6803 host cells; and (c)isolating the PHB from the recombinant Synechocystis PCC 6803 hostcells.